NUMLOCK LED blinks continuously after keyboard "disconnects"

Just this morning, I was surfing the web doing nothing in particular (other than surfing the web that is). Suddenly I heard the USB driver "sound". What's curious is that this sound wasn't one which indicated a device being ejected but one that was being newly plugged in (PROBLEM 1). Then the keyboard NUMLOCK LED light began blinking continuously.

All other devices (mouse, speaker, printer etc) were working fine. But the keyboard stopped working, except of course for that incessant blinking (PROBLEM 2). Well, I rebooted and things didn't seem to work. I unplugged both the keyboard cable and the cable which connects to the USB port ON THE KEYBOARD to other slots and it worked. I also plugged in a pen-drive to the previous two slots, and in both instances the pen worked. So I reverted the two cables of the keyboard to those slots, AND IT WORKED.

My question is what would this entail. So far the keyboard is working fine. But what could cause such an anomaly. Besides, I had NOT activated the "allow your computer to disable device" under Power Options.

Help much appreciated.

Thanks. I must mention two things here as well

1. My mouse was attached to a USB port (not these two) earlier. It stopped functioning, so had to attach it to the USB port at the front. Now the mouse also works in the previous slot.

2. The sound being emitted was one which indicates a device being PLUGGED IN, which means that (technically) the USB keyboard wasn't disconnected.

Could this indicate motherboard failure, since the mouse scenario occured almost six months back and no problem came since then. Or is it relevant to the mouse and keyboard alone (i.e. that either they are failing OR they are momentarily making me worry?)

Thanks again!